The default options (which apply when `force_ssl` is set, which is the
default in CONSUL) are `{ hsts: { subdomains: true } }`, which means we
tell browsers to apply our SSL settings to subdomains as well [1].
CONSUL installations implementing multitenancy with subdomains will
benefit from this change.
[1] https://api.rubyonrails.org/classes/ActionDispatch/SSL.html